SYDNEY (Reuters) - Australia on Thursday said it had begun an investigation to decide whether social media giant Facebook Inc <FB.O> breached its privacy laws, after the company confirmed data from 300,000 Australian users may have been used without authorization.

Personal information of up to 87 million users, mostly in the United States, may have been improperly shared with political consultancy Cambridge Analytica, Facebook said on Wednesday, exceeding a media estimate of more than 50 million.

In a statement, Australia's privacy commissioner, Angelene Falk, said her office would "confer with regulatory authorities internationally", given the global nature of the matter.

A Facebook spokeswoman in Australia said the company would be "fully responsive" to the investigation and had recently updated some privacy settings.

Facebook's chief executive, Mark Zuckerberg, told reporters during a conference call that he accepted blame for the data leak.

Zuckerberg is due to testify about the matter next week during two U.S. congressional hearings, and the data breach has drawn criticism from lawmakers and regulators around the world.

London-based Cambridge Analytica, which has counted U.S. President Donald Trump's 2016 campaign among its clients, disputed Facebook's estimate of affected users.

It said in a tweet on Wednesday that it received no more than 30 million records from a researcher it hired to collect data about people on Facebook.

Australia's investigation follows comments by New Zealand's privacy commissioner last week that Facebook had broken laws in that country, a charge the company called disappointing.

Australia's competition regulator is already investigating whether Facebook and Alphabet Inc's Google <GOOGL.O> had disrupted the news media to the detriment of publishers and consumers.